It can be seen that the UP-POPs concentrations in the ambient air around the different plants varied considerably (Table 2). Relatively high PCDD/F concentrations were found in the air samples from near plants CX and TY, and relatively high PCB concentrations were found near plants QY and SC. The UP-POPs concentrations were higher in all of the air samples collected downwind of the plants than in the samples collected upwind (Table 2). This suggests that UP-POPs concentrations in ambient air may be influenced by emissions from secondary copper and aluminum smelters.